Sliding window locks and door locks are well known. Such a lock can include a housing and pair of counter-rotating latches that rotate from a position inside the housing to engage with a strike located on the frame of the door or window on which they are installed. Such locks may be operable by means of a key to lock the door from the outside, especially where the lock is installed on a door.
Such a lock can include a manual snib or lever disposed towards the inside of the door. Such a lever allows a user to manually lock or unlock the lock once it has been locked by a key, regardless of whether the lock has been locked by the key from the outside or the inside.
However, it may not always be desirable for the door to be unlockable in this manner. For instance, a home owner may desire that the door remain locked once it has been locked by a key, so that it can only be unlocked by a user having that key. An example of such a situation is where a user is leaving their home locked while going on holiday. It would be undesirable for a burglar to be able to enter the house and unlock the door from the inside by means of the inside manual lever, thereby allowing free movement of the burglar to and from the house. In such a situation, it would be preferable that the door remain deadlocked until unlocked by a key.
It is however, desirable that the lock be operable to lock the lock from the inside by a convenient operation of the manual lever when the user is inside the house.
It is further desirable that the door is able to be deadlocked by a key from the inside or the outside in a manner that prevents unlocking of the door by the manual handle, since a house owner may find it inconvenient to have to walk around the outside of their house locking the doors.
It is further desirable that any lock that addresses the issues above be reliable in operation, and compact in construction.
In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.